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GAGING TOOLS AND
METHODS

MEASURING INSTRUMENTS IK: ED BY MACHINISTS
AND TOOLMAKERS

BY FRANKLIN D. JONES

MACHINERY'S REFLREuCE BOOK NO. 130
PUBLISHED BY MACHINEKi NEW YORK

MACHINERY'S REFERENCE SERIES

EACH NUMBER IS A UNIT IN A SERIES ON ELECTRICAL AND

STEAM ENGINEERING DRAWING AND MACHINE

DESIGN AND SHOP PRACTICE

NUMBER 130

GAGING TOOLS AND
METHODS

By FRANKLIN D. JONES

CONTENTS

Classes and Standards of Measurement - - - - 3

Calipers and Micrometers 6

Fixed and Adjustable Gages 20

Miscellaneous Measuring and Gaging Tools - - - 30

• -J*:

CHAPTER I

CLASSES AND STANDARDS OP MEASUREMENT

This treatise deals with the various forms and types of gages and
measuring instruments used in machine shops and tool-rooms. Prac-
tically all of the measuring tools used by machinists and toolmakers
may be divided into two general classes ; viz., the tools for measure-
ments of length, and those for the measurement of tapers or angles.
Length measurements, in turn, may be divided into line 'measure-
ments and end measurements. The former are made by direct com-
parison with graduations on the measuring tool, and the latter by
bringing the work into actual contact with 'the measuring surfaces of
the instrument. Examples of line measurement are those made with
a machinists' rule, whereas, end measurements are those made with
a micrometer or similar tool. Angular measurements are also ob-
tained either directly by means of degree graduations on an adjust-
able protractor, or by testing the work with a gage which conforms
to the required angle.

In the two general classes of tools for length and angular measure-
ments, there are many different types and designs. For instance,
there is the adjustable type, which is graduated and is used for taking
direct measurements in inches or degrees; then, there is another type
which is fixed and cannot be used for determining various sizes or
angles, but simply for gaging or testing one particular size. There are
also tools for taking approximate measurements and others designed
for very accurate or precise measurements. Ordinarily, both classes
of measurements would be required in building a machine or tool,
because some parts must be accurate, whereas others can vary in size
to some extent, and, in such cases, any unnecessary refinement means
an increase of time and cost. Measurements which, in machine and
tool construction, belong in the approximate class, are those made by
means of a rule or scale, or by working to lines which have been laid
out on the work and represent finished surfaces. For precise meas-
urements, there are vernier calipers, micrometers, fixed gages, and
reference gages which represent subdivisions of the standard yard
within very small limits.

Standards of Measurement

Evidently, if there is to be a uniform system of measurement, it
is necessary to have a fixed standard. The yard is the commonly
accepted standard of length in the United States, although it is not
the legal standard. In 1866 Congress passed a law making legal the
meter. In 1875 .representatives of various countries signed a treaty
providing for the establishment and maintenance, at the common
expense of the contracting nations, of a scientific and permanent

347594

4 No. 130— GAGING TOOLS AND METHODS

bureau of weights and measures, to be located in Paris. This bureau
was empowered to construct and preserve the international standards
and to distribute copies to the different countries.

The international meter adopted by this Bureau is the fundamental
unit of length in the United States. The primary standard is de-
posited at the International Bureau of Weights and Measures near
Paris, France. This is a platinum-iridium bar with three fine lines
at each end; the distance between the middle lines of each end, when
the bar is at a temperature of 0 degrees C., is one meter by definition
Two copies of this bar are in the possession of the United States and
are deposited at the Bureau of Standards, in Washington.

3600
The United States yard is defined by the relation, 1 yard =

3937

meter. The legal equivalent of the meter for commercial purposes
was fixed as 39.37 inches by law in July, 1866, and experience having
shown that this value was exact within the error of observation, the
United States office of standard weights and measures was, by executive
order, in 1893, authorized to derive the yard from the meter by the
use of this relation. No ultimate standard of reference for angular
measurements is required, inasmuch as the degree can be originated
by subdivision of the circle.

The Bureau of Standards employs various methods of making com-
parisons of bars which are submitted by manufacturers for test, the
method depending upon the kind of bar, the accuracy desired, and the
adaptability of the apparatus available to the bar or test piece. Thus,
there are several classes of tests, such as Class A, for reference stand-
ards, Class B, for working standards, etc. The fee charged for this
work depends, of course, upon the class and nature of the test. Metric
length measures tested by the bureau are standardized at 20 degrees
C., and standards in the customary units of yards, feet, and inches are
made to be correct at 62 degrees F.

Value of a Standard of Measurement

The standard bars at Washington are the ultimate standard of
reference for the manufacturers in this country. Working standards
or duplicates have been made for the use of manufacturers of gages
and measuring instruments. In 1893, the Brown & Sharpe Mfg. Co.
decided to make a new standard to replace the one they had at that
time. The following general description of how a copy of the govern-
ment standard was made is taken from a paper by Mr. W. A. Viall,
presented before the Providence Association of Mechanical Engineers,
and shows the great accuracy necessary in connection with work of
this kind.

First steel bars about 40 inches long and I1/! inch square were
planed, and then allowed to "season" for several months. At the ends
of these bars two gold plugs were inserted with centers 36 inches
apart, and a little beyond these, two other plugs 1 meter apart. This
bar was placed in position upon a heavy bed so arranged that a tool

STANDARDS OF MEASUREMENT 5

carrier could pass over the bar. The tool carrier consisted of a light
frame-work holding the marking tool. The point of this marking tool
was curved and had an angle, so that if dropped, it made an im-
pression in the form of an ellipse. A line made with this tool was
short and that portion of the line was used which passed, apparently,
through the straight line in the eyeglass of the microscope. In order
to make these lines as definite as possible, the point was lapped to a
bright surface. A microscope at the front of the tool carrier was set
to coincide with the graduation on the standard bar from which the
new bar was to be graduated. After obtaining this setting, the mark-
ing tool was dropped by turning a lever, thus making a line on the
plugs that was so fine it was not visible to the naked eye. After mak-
ing this first line the carriage and marker was moved along to co-
incide with the other line on the standard, and after the correction had
been made by the use of a micrometer in the microscope, the mark-
ing tool was again dropped, giving a second line which was intended
to mark the distance equivalent to one yard. This same operation
was repeated in marking lines representing the meter. This work
was done, of course, with the greatest care, and while it may appear
very simple from the description, it required a great deal of time
and patience.

The standard bar thus marked was taken to Washington and com-
pared with the government standard Bronze No. 11 and also with
Low Moor iron No. 57. In comparing these standards, a method was
employed very similar to that used in marking. The bar, properly
supported, was placed upon a box that rested upon rolls and on this
same box was placed the government standard with which the Brown
& Sharpe standard was to be compared. Both the government standard
and the bar to be tested were placed in position under the microscope
and by the micrometer screw of the microscope the variation between
the two was measured. Three comparisons or tests were made on each
end before determining the reading of the microscope, and after these
comparisons the value of the B. & S. standard No. 2 was found to be
36.00061 inches for the yard, and 1.0000147 meter for the meter.

After completing this work, a second standard known as No. 3 was
prepared, and comparison with the government standard showed the
error to be 0.00002 inch for the yard, and 0.000005 meter for the meter.
After establishing a yard in this manner, the next problem was that
of obtaining an inch; this was done by subdividing the yard into two
equal parts, and then further subdividing these two divisions into
three, and the three into six, thus giving thirty-six subdivisions or
inches. ••'•:

CHAPTER II

CALIPERS AND MICROMETERS

Calipers are used principally for external and internal measure-
ments not requiring great accuracy, and are made in a variety of
designs. Sketch A, Pig. 1, shows outside calipers and indicates how
they are used for testing the size of a cylindrical part. Inside calipers
for testing the diameter of a hole are shown at B, and sketch C illus-
trates how' the outside calipers are set by comparison with the inside
pair or vice versa. For instance, if the shaft at A were being fitted to
the hole B, the calipers would be set as follows: First the inside pair
would be adjusted to just touch both sides of the hole, when held as
shown. The outside calipers would then be set to just touch the ends
of the inside calipers so that the outside pair, practically speaking,
~would represent the hole and could be used for testing the size of
the shaft. Obviously, if a rather heavy pressure were required to
force the outside calipers over the shaft, this would indicate that the
diameter was too large. If the pressure were the same as between
the two pairs of calipers, the shaft would fit tightly; whereas, if the
calipers passed over easily and without perceptible pressure, a close
sliding fit should be obtained.

Evidently, when testing sizes by means of calipers, the degree of
accuracy attained depends largely upon the skill, judgment and ex-
perience of the one who sets and uses the calipers. Some machinists
can work within very close limits, whereas others lack the delicate
sense of touch that is necessary. In order to eliminate this personal
factor, micrometers are extensively used in order to obtain direct
measurements and secure different classes of fits by a definite allow-
ance in thousandths of an inch, instead of by judging the allowance
from the pressure or side play of the calipers. Fixed gages, which
are accurately made to the sizes required, are also widely used,
especially for testing duplicate parts in connection with interchange-
able manufacture.

Most calipers are either the firm joint or the spring type; the
former, which is shown in Fig. 1, simply has a friction joint between
the two "legs," whereas the spring type (illustrated in Fig. 3) is pro-
vided with an adjusting screw and nut, and the two members are
forced together against the tension of the curved spring at the upper
or pivot end. These are merely constructional features and have
nothing to do with the use of the calipers. Spring calipers are not
made in large sizes like the friction-joint type.

Hermaphrodite and Shoulder Calipers

The caliper illustrated at A, Fig. 2, is half caliper and half divider.
This form is often used for drawing a line parallel to a finished edge

CALIPERS

(as the illustration indicates) or for locating a central point on the
end of a shaft by setting the caliper to the radius of the shaft, as near
as can be judged, and then scribing arcs which, at the point of inter-
section, indicate the center.

The special form of caliper shown at B is useful either for testing
the distance from the end of a shaft or rod to a shoulder, or the dis-
tance from one shoulder to another. This type of caliper is also con-
venient for testing the diameter when boring a cylindrical surface
{such as the crown-brass of a locomotive driving box) which does not
extend through a half circle, thus making it impossible to measure

Machinery

Fig. 1. Outside and Inside Calipers

the diameter of the cut directly. In the case of the driving box, the
caliper points are set to the diameter of the journal and the size of
the bore is tested by calipering from the point of the boring tool to
the bored surface, when the box is turned around to locate the bear-
ing brass away from the tool. Evidently, when the work is in this
position, the distance from the cutting edge to the bored surface
represents the diameter of the cut.

No. 130— GAGING TOOLS AND METHODS

Thread Calipers

The spring type of calipers shown at A and B, Fig. 3, are used for
measuring the diameters of threads. Caliper A is for testing the out-
side diameter. It has broad ends which span two or more threads so
that the diameter across the tops of the threads can easily be obtained
by first adjusting the calipers to just touch the threads and then meas-
uring the distance beween the ends with a machinist's rule. Calipar
B is for testing the diameter at the bottom or root of the thread. The
ends are V-shaped so that the points will bear at the bottom of the
thread groove. For accurate measurements a thread micrometer
should be used. (See "Thread Micrometer.")

While the principal types of ordinary calipers have been referred
to in the foregoing, other forms are often used. For some classes of
work, combination calipers are very convenient. This type usually

Machinery

Fig. 2. (A) Hermaphrodite Calipers (B) Shoulder Calipers

combines dividers and outside and inside calipers in one tool. There
are also many other special forms, many of which are made by
machinists, for taking measurements under unusual conditions which
make it impossible to use ordinary calipers.

Points on Setting Calipers

The accuracy of caliper measurements is governed partly by the
adjustment of the calipers and also by the skill or judgment of the
workmen in...transifixring-this. size to the work. Outside calipers are
commonly set to a given dimension in inches, by holding one end
against the end of a scale and adjusting the other end until it coin-
cides with the graduation line representing the required size. A more

CALIPERS

accurate and positive method is to use a standard plug or disk gage
of the required diameter, if one is available.

When setting inside calipers with a scale, the end of the latter
should be placed squarely against some true surface; then one end
of the caliper is held against this same surface, thus aligning it with
the end of the scale, while the other end is adjusted to the required
measurement. To insure a square end against which to place a scale
and caliper, some machinists hold the scale on the blade of the square
with one end resting against the beam or stock.

Standard ring gages or an outside micrometer are preferable for
setting inside calipers. A ring gage of the required diameter is not
always available, but an outside micrometer is a common tool, and,

Machinery

Fig. 3. Thread Calipers of Spring Type

being adjustable, affords an accurate method of setting inside calipers.
The micrometer is first set to the size required; then the ends of the
caliper are adjusted to just touch the parallel faces of the anvil and
spindle of the micrometer. When an attempt is made to set inside
calipers to a given measurement, by first setting outside calipers with
a scale and then transferring the size to the inside calipers, obviously,
several chances of error are introduced.

Side Play of Calipers

Judging a fit allowance by the amount of side play the calipers have
in a hole, is a common method, although not very reliable, especially
when considerable accuracy is necessary. To illustrate this method
of fitting, suppose a pulley hub were being bored to fit a shaft. After
setting the outside calipers to the size of the shaft, the inside calipers
should be adjusted to the outside pair, so that the bearing or degree
of contact is the same as between the outside calipers and the shaft.

No. 130— GAGING TOOLS AND METHODS

The hole should then be bored to such a diameter that the inside
calipers have a slight side play, in order to provide an easy sliding fit
for the shaft

The amount of this side play would depend upon the diameter and
length of the hole and the accuracy required for the fit. For instance,
a side play of only y8 inch might be sufficient for a small size hole,
whereas, y2 inch or more might be necessary for a comparatively
large hole, especially if quite long. The following rule may be used
to determine the allowance for a given amount of side play, or, in
other words, the difference between the diameter of the hole, and the

ALLOWANCES FOR DIFFERENT CLASSES OF FITS*

Diameter, Inches

Running Fits

Push Fits

Uptoi
itol
1 to 2
2 to 3
3 to 4
4 to 5
5 to 6

-0.00075 to -0.0015
-0.001 to -0.002
-0.0015 to -0.0025
-0.0015 to —0.003
-0.002 to -0.0035
-00025 to -0.004
-0.0025 to -0.0045

-0.00025 to -0.00075
-0.0005 to -0.001
-0.0005 to -0.0015
-0.0005 to -0.0015
-0.00075 to -0.002
-0.00075 to -0.002
-0.00075 to -0.002

Diameter, Inches

Driving Fits

Forced Fits

Uptoi
I tot

1 to 2
2 to 3
3 to 4
4 to 5
5 to 6

+0.0004 to +0.0006
+0.0005 to +0.001
+0.00075 to +0.002
+0.0015 to +0.003
+0.002 to +0.004
+0.002 to +0.0045
+0.003 to +0.005

+0.0005 to +0.001
+0.001 to +0.003
+0.002 to +0.004
+0.003 to +0.006
+0.005 to +0.008
+0.006 to +0.010
+0.008 to +0.012

* These allowances are intended for average machine work. If the bearings are long
the allowances for running fits may have to be increased.

dimensions to which the calipers are set or the length of a standard
end-measuring rod.

Rule: Determine the amount of side play in sixteenths of an inch
or the number of sixteenths; square this number and divide the result
by twice the dimension to which the calipers are set, or by twice the
length of the end-measuring rod. The quotient represents the allow-
ance or difference in thousandths of an inch.

For example, suppose a standard end-measuring rod, 6 inches long,
had a side play of ^4 inch in a bored hole. What is the difference
between the length of the rod and the diameter of the hole?

In i/4 inch, there are 4 sixteenths; hence, the allowance or difference

4X4 16

— = — =1.3 thousandths or 0.0013 inch.
2X6 12

While this method does not give results which are absolutely ac-
curate, the error is so small, especially when the amount of side play
is small, that it can usually be disregarded. Judging an allowance for

VERNIER CALIPER

a fit in this way, however, is not to be recommended, and, in most
shops, would be unnecessary, owing to the gages and micrometers for
both external and internal measurements which are now in common
use and give direct measurements.

A general idea of the allowances required for average machine work
may be obtained from the table on page 10, which covers four dif-
ferent classes of fits and diameters varying from 0 to 6 inches.

The Vernier Caliper

The vernier is an auxiliary scale that is attached to vernier calipers,
height gages, depth gages, protractors, etc., for obtaining the frac-
tional parts of the subdivisions of the true scale of the instrument.
When a scale is graduated in hundredths or even sixty-fourths of an
inch, it is confusing to take measurements with it owing to the fine-
ness of lines. If it were possible to graduate a scale to thousandths,

Machinery

Fig. 4. Vernier Caliper

or with every inch subdivided into a thousand equal parts, such a
scale would, of course, be useless, owing to the extreme fineness of
the lines and the minute distances between them. Such fine divisions
on a scale are not, however, necessary, for by means of the vernier
scale, graduations which are comparatively large can be divided so
that fine measurements may be taken.

For example, the true or regular scale of the vernier caliper shown
in Fig. 4, is graduated in fortieths of an inch, but by means of the
vernier scale V, which is attached to the sliding jaw of the instru-
ment, measurements within one-thousandth of an inch can be taken.
In other words, the vernier, in this case, makes it possible to divide
each fortieth of an inch on the true scale into twenty-five parts. To
measure the diameter D with a vernier caliper, adjust the sliding jaw
until it is close to the work and then lock the slide A by the screw

No. 130— GAGING TOOLS AND METHODS

shown. With the nut B, which is used for making fine adjustments,
move the jaw until it just touches the work. The distance that the
vernier scale zero has moved to the right of the zero mark on the
true scale (which equals diameter Z>) is then read directly in
thousandths of an inch, by calling each tenth on the true scale that
has been passed by the vernier zero, one hundred thousandths, and
each fortieth twenty-five thousandths, and adding to this number as
many thousandths as are indicated by the vernier. The vernier zero
in the illustration is slightly beyond the five-tenths division; hence,
the reading is 0.500 plus the number of thousandths indicated by that

024

Machinery

Figr. 5. Scales -with Verniers set in Different Positions

line on the vernier that exactly coincides with one on the scale which,
in this case, is line 15, making the reading 0.500 + 0.015 = 0.515 inch.

Principle of the Vernier Scale

By referring to the enlarged scales shown at A and B, Fig. 5, the
principle of the vernier will be more apparent. When a vernier
caliper reads to thousandths of an inch, each inch of the true scale 8
is divided into ten parts, and each tenth into four parts, so that the
finest divisions are fortieths of an inch. The vernier scale V has
twenty-five divisions, and its total length is equal to twenty-four
divisions on the true scale, or 24/40 of an inch; therefore, each
division on the vernier equals 1/25 of 24/40 or 24/1000 inch. Now,
as 1/40 equals 25/1000, we see that the vernier divisions are 1/1000
inch shorter than those on the true scale. Therefore if the zero
marks of both scales were exactly in line, the first two lines to the
right would be 1/1000 inch apart; the next two 2/1000, etc. It is
evident, then, that if the vernier were moved to the right until, say,

VERNIER CALIPER 13

the tenth line from the zero mark exactly coincides with one on the
true scale, as shown at A, the movement would be equal to 0.010 inch,
since this line was 0.010 inch to the left of the mark with which it
now coincides, when the zero lines of both scales were together.
Similarly, if the fifteenth line were exactly opposite a line on the true
scale, the movement of the vernier would be equal to 0.015, etc.; so
we see that the number of thousandths that the vernier zero has
moved past a graduation on the true scale is determined simply by
counting the number of spaces between the zero of the vernier, and
that line on it which exactly coincides with one on the true scale.
If the vernier were moved along to the position shown by the next
sketch B (Fig. 5) the true scale would indicate directly that the
reading was slightly over 0.500 inch, and the coincidence of the gradu-
ation line 15 on the vernier with a line on the true scale, would show
the exact reading to be 0.500 + 0.015 = 0.515 inch.

In Fig. 5 a true scale S is shown at C that is graduated into six-
teenths of an inch, and the vernier V has eight divisions with a total
length equal to seven divisions on the true scale, or 7/16 of an inch;
therefore, each division on the vernier is 1/8 of 1/16, or 1/128 inch
shorter than the divisions on the true scale; so we see that in this
case the vernier enables readings to be taken -within one hundred and
twenty-eighths of an inch, instead of in thousandths as with the one
previously described. The divisions then that may be obtained by a
vernier depend altogether on the way the true and vernier scales are
graduated.

In order to determine the fractional part of an inch that may be
obtained by any vernier, multiply the denominator of the finest sub-
division of an inch given on the true scale by the total number of
divisions on the vernier. For example, if (as in Fig. 4) the true scale
is divided into fortieths and the vernier into twenty-five parts, the
vernier will read to thousandths (40X25 = 1000). If there are six-
teen divisions to the inch on the true scale and a total of eight on the
vernier, the latter will enable readings within one hundred twenty-
eighths of an inch to be taken (16 X 8 = 128). It will be seen then
that each subdivision on the true scale can be divided into as many
parts as there are divisions on the vernier.

The following is a general rule for taking readings with a vernier:
Note\^ the number of inches and whole divisions of an inch that the

vernier zero has moved along the true scale, and then add to this\
number as many thousandths, or hundredths, or whatever fractional
part of an inch the vernier reads to, as there are spaces between the
vernier zero and that line on it which coincides with one on the true
scale.

The vernier caliper can be used for measuring the diameters of
holes or for other inside measurements, as well as for external meas-
urements, by using the outside surfaces of the jaws or measuring
points. The width of the jaws should be added to the apparent read-
ing as given by the scale and vernier, to obtain the correct inside

No. 130— GAGING TOOLS AND METHODS

dimensions. No such allowance is necessary when using the gradua-
tions on the opposite side of the beam of some vernier calipers, as two
lines marked "in" and "out" indicate inside and outside maesurements.

Vernier Caliper with Metric Graduations

The application of the vernier to a caliper graduated on the metric
system is illustrated in Fig. 6. In this case we have, instead of inches,
centimeters which are subdivided into ten parts called millimeters.
By the aid of the vernier, each millimeter is again divided into ten
parts so that readings can be taken to within 1/10 of a millimeter or
1/100 of a centimeter (0.0039 of an inch). The reading with the
caliper set as shown in the illustration is 2 55/100 centimeters, or, as
commonly expressed, 25 5/10 millimeters. As shown more clearly by
the enlarged detail view, the left-hand or zero mark of the vernier has

Machinery

Figr. 6. Vernier Caliper Graduated on Metric System

passed the 2y2 centimeter graduation, and the fifth line on the vernier
coincides with one on the true scale; therefore, the reading is 25 milli-
meters plus 5/10 of a millimeter. This particular instrument has on
the opposite side of the beam two series of inch graduations which,
with the verniers, enable measurements within 1/100 and 1/128 of an
inch to be taken. Therefore inches may be converted into metric
measurement, and vice versa, by taking the reading first on one side
of the beam and then on the other.

Micrometers for External and Internal Measurements
Micrometer calipers are used for taking accurate measurements. A
small size for external measurements is shown at A, Fig. 7. The part
to be measured is placed against the anvil a and the adjustable
spindle b is then screwed in until it bears lightly against the work,
by turning the thimble or sleeve c; the size is then determined by
referring to the micrometer graduations. Most micrometers are gradu-
ated to read to thousandths of an inch, although some have an
auxiliary vernier scale which enables readings to within 0.0001 inch to

MICROMETERS

be taken. (The method of reading a micrometer will be explained
later.) This particular micrometer will measure all sizes varying
from 0 to 1 inch. Some outside micrometers have a lock-nut which
is used to clamp the spindle in order to convert the micrometer into
a fixed gage. To use a micrometer in this way is generally con-
sidered poor practice. The proper method of taking a measurement
is to close the contact points against the work with a light pressure
and then determine the size by the graduations as previously
explained.

Many micrometers have what is called a ratchet stop d at the end
of the barrel or thimble. If this is used when adjusting the measur-
ing point against the work, it will slip when the point bears lightly,
and thus prevent excessive pressure. The advantage of securing a

Machinery

Fig. 7. Outside and Inside Micrometers

uniform contact or degree of pressure is that uniform readings are
then obtained. Obviously, a difference in pressure will give a dif-
ferent reading and might result in a serious error. Inaccuracies from
this cause might be negligible so far as one workman is concerned,
but they become important where measurements are taken by many
different workmen, because everyone does not have the same sense
of touch.

A micrometer for measuring the diameters of holes or for taking
other internal dimensions is shown at B, Fig. 7. The measuring sur-
faces are hardened and ground to a radius to secure accurate measure-
ments and to avoid cramping when measuring the distances between
parallel surfaces. The movable jaw has a clamp screw that is
tightened when it is desired to retain the setting of the calipers.

Another form of inside micrometer is shown in Fig. 8. This par-
ticular size can be used for measurements varying from 2 to 12
inches. When testing the diameter of a comparatively small hole,

No. 130— GAGING TOOLS AND METHODS

when there is not sufficient room for the hand, an auxiliary handle a
is screwed into the micrometer head as shown in the illustration. The
micrometer screw has a movement of one-half inch and by inserting
extension rods of different lengths in the. head at &, any dimension
up to 12 inches can be obtained. Two of these extension rods are
shown to the right. They are provided with collars which serve to
locate them accurately in the micrometer head.

An inside micrometer gage that is especially adapted for large
internal measurements is shown at A, Fig. 9. This gage consists of
a holder equipped with a micrometer screw with graduations read-
ing to 0.001 inch, and into this holder is inserted an adjustable rod.
This rod also has graduations in the form of a series of annular
grooves of a form and depth that allow clamping fingers on the holder
to spring into them, thus making it possible to shift the rod in or
out to the required length. Gages of this type usually have a series

Machinery

Fig. 8, Inside Micrometer equipped with Extension Rods

of rods so that a wide range of sizes can be measured. They are not
only used for internal measurements but for setting calipers and for
similar work.

A micrometer ealiper for large external measurements is shown at
B. The micrometer screw has an adjustment of one inch and is
graduated to read to 0.001 inch. When measuring small sizes, the long
anvil or spindle s is used, whereas, for larger sizes, one of the shorter
spindles is inserted. The sides of the steel frame are covered with
hard rubber to prevent inaccuracies in the measurements as the result
of expansion from the heat of the hands. As will be noted, this
micrometer has a ratchet stop to insure uniform pressure when
measuring.

Thread Micrometers

For the accurate measurement of screws or threads, the special
thread micrometer shown in Fig. 10 is often used. The fixed anvil is
V-shaped so as to fit over the thread, while the movable point is cone-
shaped so that it will enter the space between two threads. The con-

MICROMETERS

tact points are on the sides of the thread, as they must be in order
that the pitch diameter may be determined. The cone-shaped point of
the measuring screw is slightly rounded so that it will not bear at
the bottom of the thread. There is also sufficient clearance at the
bottom of the V-shaped anvil to prevent it from bearing on the top of
the thread. The movable point is adapted to measuring all pitches,
but the fixed anvil is limited in its capacity. To cover the whole range
of pitches, from the finest to the coarest, a number of fixed anvils are
required.

To find the theoretieal pitch diameter, which is measured by the
micrometer, subtract the single depth of the thread from the standard
outside diameter. The depth of a V-thread equals 0.866 -j- number of

Machinery

Fig. 9.

(A) Inside Micrometer Gage for Large Holes
(B) Large Outside Micrometer

threads per inch, and depth of U. S. standard thread equals 0.6495
-f- number of threads per inch.

If standard plug gages are available, it is not necessary to actually
measure the pitch diameter, but merely to compare it with the
standard gage. In this case, a ball-point micrometer such as is shown
in Fig. 11 may be employed. Two types of ball-point micrometers
are ordinarily used. One is simply a regular micrometer with ball
points made to slip over both measuring points, as shown by the detail
sketch B. This makes a combination plain and ball-point micrometer,
the ball points being easily removed. These ball points, however,
may not fit solidly on their seats and are apt to cause errors in the
measurements. The best method is to use a regular micrometer into
which ball points have been fitted as shown at A. Care should be
taken to have the ball point in the spindle run true. A hole is pro-
vided in the spindle so that the ball point can easily be driven out
when a larger or smaller size of ball point is required.

No. 130— GAGING TOOLS AND METHODS

How to Read a Micrometer

The pitch of the thread on the spindle b (Fig. 7) of an ordinary
micrometer is 1/40 of an inch. Along the frame at e (see also detail
sketch A, Pig. 12), there are graduations which are 1/40 inch apart;
therefore, when thimble c and the measuring spindle are turned one
complete revolution, they move in or out, a distance equal to one of

Machinery

Tig. 10. Thread Micrometer

the graduations or 1/40 inch, which equals 25/1000 inch. It is evident
then that if instead of turning the thimble one complete revolution,
it is turned say 1/25 of a revolution, that the distance between the
anvil and the end of the spinclle will be increased or diminished 1/25
of 25/1000 of an inch, or one thousandth inch; therefore, the beveled
edge of a micrometer spindle has twenty-five graduations, each of

Machinery

Tig. 11. Ball-point Thread Micrometer

which represents 0.001 inch. Following is a general rule for reading
a micrometer:

Count the number of whole divisions that are visible on the scale
of the frame, multiply this number by 25 (the number of thousandths
of an inch that each division represents) and] add to the product the
number of that division on the thimble which coincides with the axial

MICROMETERS

zero line on the frame. The result will be the diameter expressed in
thousandths of an inch.

As the numbers 1, 2, 3, etc., opposite every fourth subdivision on
the frame indicate hundreds of thousandths, the reading can easily be
taken mentally. Suppose the thimole were screwed out so that
graduation 2, and three additional subdivisions were visible (as shown
at A, Fig. 12), and that graduation 10 on the thimble coincided with
the axial line on the frame. The reading then would be 0.200 + 0.075
+ 0.010, or 0.285 inch.

Some micrometers have a vernier scale v on the frame (see sketch
B, Fig. 12) in addition to the regular graduations, so that measure-
ments within 0.0001 inch can be taken. Micrometers of this type are
read as follows:

First determine the number of thousandths, as with an ordinary
micrometer, and then find a line on the vernier scale that exactly cO-

C-l

98765432

Machinery

Fig. 12. Micrometer Graduations

incides with one on the thimble; the number of this line represents
the number of ten-thousandths to be added to the number of thous-
andths obtained by the regular graduations.

The relation between the graduations of the vernier and those on
the thimble is more clearly shown by diagram C. The vernier has ten
divisions which occupy the same space as nine divisions on the thimble,
and for convenience in reading are numbered as shown. The dif-
ference between the width of a vernier division and one on the
thimble is equal to one-tenth of a space on the thimble. Therefore a
movement of the thimble equal to this difference between the vernier
and thimble graduations represents 0.0001 inch. When the thimble 0
coincides with the lin.e x on the frame, the 0 of the vernier coincides
with the third line to the left (marked with an asterisk). Now when
the thimble 0 (or any other graduation line on the thimble) has
passed line x, the number of ten-thousandths to add to the regular
reading is equal to the number of that line on the vernier which
exactly coincides with a line on the thimble. Thus the reading shown
at C (Fig. 12) is 0.275 + 0.0004 = 0.2754 inch.

CHAPTER III

FIXED AND ADJUSTABLE GAGES

Strictly speaking, any tool or instrument used forsaking measure-
ments might properly be called a gage, but this term, as used by
machinists and toolmakers, is generally understood to mean that class
of tools which conform to a fixed dimension and are used for 'testing
sizes but are not provided with graduated adjustable members for
measuring various lengths or angles. There are exceptions, however,
to this general classification.

Measuring instruments, such as the micrometer and vernier caliper,
are indispensable because they can be used for determining actual

Machinery

Fig. 13. (A) Snap Gage (B) Internal and External Gage

dimensions, and, being adjustable, cover quite a range of sizes. Any
form of adjustable measuring tool, however, has certain disadvantages
for such work as testing the sizes of duplicate parts, especially when
such tests must be made repeatedly, and solid or fixed gages are
commonly used. There is less chance of inaccuracy with a fixed gage
and it is more convenient to use than a tool which must be adjusted,
but owing to the necessity of having one gage for each variation in
size, and because of the cost of a set covering a wide range of sizes,
solid gages are used more particularly for testing large numbers of
duplicate parts in connection with interchangeable manufacture.

Two different types of fixed gages are shown in Fig. 13. The form
shown at A is commonly known as a "snap gage." The distance be-

GAGES

tween the measuring surfaces is fixed and represents the size stamped
upon the gage, within very close limits. This type of gage can be
obtained in various sizes and is used for measuring duplicate parts
in connection with general shop work. As a gage of this kind is
repeatedly passed over the work, it becomes worn, and, therefore,
should be compared or tested occasionally with a standard reference
plug or disk. In case of excessive wear, the gage can be closed in
slightly smaller than the required size and then be reground or
lapp'ed to the original size, as shown by a reference gage.

Sketch B illustrates another form of snap or caliper gage. This is
double-ended and is intended for both external and internal measure-

Machinery

Tig. 14. External and Internal Limit Gages

ments, the width of the internal end being the same as the distance
between the measuring surfaces of the external end.

Limit Gagres

With the modern system of interchangeable manufacture, machine
parts are made to a definite size within certain limits which are varied
according to the accuracy required, which, in turn,, depends upon the
nature of the work. In order to insure having all parts of a given
size or class, within the prescribed limit so that they can readily be
assembled without extra and unnecessary fitting, what are known as
"limit gages" are used. One form of limit gage for external measure-
ment is shown at A, Fig. 14. It is double-ended and has a "go" end
and a "not go" end; that is, when the work is reduced to the correct
size, one end of the gage will pass over it but not the other end: When
a single-ended snap gage A, Fig. 13, is used, the diameter of the work
may be slightly less than it should be, but by having a gage for the
minimum as well as for the maximum size, every part must come

No. 130— GAGING TOOLS AND METHODS

within the limits of the gage. This allowance or limit is made to con-
form to whatever amount experience has shown to be correct for the
particular class of fit required.

Another external limit gage is shown at B, Fig. 14. Nominally this
is a i/4 inch gage. The size of the "go" end is 0.250 inch and the size
of the "not go" end is 0.2485 inch; hence the tolerance is 0.0015 inch.
Therefore a part that is more than 0.0015 inch less than 0.250 inch will
not pass the "not go" end of the gage.

An internal limit gage is shown at C. The nominal size of this par-
ticular gage is I1/! inch. The diameter of the "go" end is 1.2492 inch,
whereas the diameter of the "not go" end is 1.2506 inch; hence, in
this case, the tolerance equals 1.2506 — 1.2492 = 0.0014 inch. Inci-
dentally, it is good practice to make all holes to standard sizes within

Machinery

Fig. 15. (A) Adjustable Limit Gage; (B) Limit Gage with
Fixed Points

whatever limits may be advisable, and vary the size of the cylindrical
parts to secure either a forced fit, running fit, or whatever class of fit
may be required.

It will be noted that the ends of these limit gages are of different
shape so that the large and small sizes can readily be identified with-
out referring to the dimension stamped on the gage ends. Limit gages
are very generally used for the final inspection of machine parts, as
well as for testing sizes during the machining process. They are
superior to the micrometer for many classes of inspection work, be-
cause the adjustment and reading necessary with a micrometer often
results in slight variations of measurement, especially when the read-
ings are taken by different workmen.

Adjustable Limit Snap Gage

The snap gage shown at A, Fig. 15, differs from the ordinary single-
ended type in two particulars: In the first place, it has two sets of
measuring plugs and is a limit gage. The lower set forms the "go"
end and the upper set the "not go" end. These plugs are also adjust-
able so that when the gage becomes inaccurate, as the result of wear,

GAGES

the plugs can easily be reset, a standard reference gage being used to
determine the distance between them.

The plugs are plain cylinders of hardened steel and are lapped to
a snug sliding fit in the hole of the gage body. The ends are square
and bear against adjusting screws, the forward ends of which are also

Machinery

Fig. 16. (A) Plug and Ring Gages (B) Internal and External
Thread Gages

lapped square. The clamping screws at the side not only clamp the
plugs but tend to force them against the adjusting screws. The handle
has an insulated grip.

Another snap gage of the limit type is shown at B. This gage has
fixed points which can be renewed in case of wear.

Machinery

Fig. 17. Internal and External Taper Gages

Plug and Ring- Gages

A standard external or ring gage and internal or plug gage is
shown at A, Fig. 16. These gages are very accurately made and are
used either as reference gages or for setting calipers, etc., or as work-
ing gages. One gage manufacturer makes solid gages of this type in
diameters varying from 1/16 inch to 3 inches. For larger sizes, up
to 6 inches in diameter, the plug gages are made hollow.

No. 130— GAGING TOOLS AND METHODS

U. S. standard thread gages are shown at B, Fig. 16. These gages
are intended as a practical working standard. The internal gage or
plug is a standard to which the external templet is adjusted. The
plain unthreaded end of the plug gage is ground and lapped to the
exact diameter at the root or bottom of the thread.

Gages for testing the accuracy of tapers are shown in Fig. 17. The
ring gage A is used for external tapers and the plug B for holes. The
plug accurately fits the ring and when they are assembled, a line on
the plug coincides with the end of the ring. This line is used for
gaging the depth of holes which must conform to the standard size
of the ring gage. When the plug gage is used as a working gage in
the shop, the ring is usually kept as a reference gage. On the other

Machinery

Fig. 18. Disk Gage for Originating or Accurately Measuring
Tapers or .Angles

hand, if a ring is used for testing external tapers, the plug is often
preserved as the reference gage.

Gagre for Origrinatingr and Accurately Measuring: Tapers
When a certain taper or angle must be originated or accurately
measured, the disk type of gage shown in Fig. 18 may be employed.
The principle of the disk method of taper measurement is that if two
disks of unequal diameters are placed either in contact or a certain
distance apart, lines tangent to their peripheries will represent an
angle or taper, the degree of which depends upon the diameters of
the two disks and the distance between them. This gage consists of
two adjustable .straight-edges A and A,, which are in contact with disks
B and Jffj. The angle a or the taper between the straight-edges de-
pends, of course, upon the diameters of the disks and the center dis-
tance C, and as these three dimensions can be measured accurately, it
is possible to set the gage to a given angle within very close limits.
Moreover, if a record of the three dimensions is kept, the exact setting
of the gage can easily be reproduced at any time. The following rules
may be used for adjusting a gage of this type.

GAGES 25

To Find Center Distance for a Given Angle. — When the straight-
edges must be set to a given angle a, to determine center distance C
between disks of known diameter. Rule: Find the sine of half the
angle a in a table of sines; divide the difference between the disk
diameters by double this sine.

Example: — If an angle a of 20 degrees is required, and the disks
are 1 and 3 inches in diameter, respectively, find the required center
distance C.

— =10 degrees; sin 10° = 0.17365;
2
3 — 1

= 5.759 inches = center distance C.

2 X 0.17365

To Find Center Distance for a Given Taper. — When the taper, in
inches per foot, is given, to determine center distance C. Rule: Divide
the taper by 24 and find the angle corresponding to the quotient in a
table of tangents; then find the sine corresponding to this angle and
divide the difference between the disk diameters by twice the sine.

Example: — Gage is to be set to % inch per foot, and disk diameters
are 1.25 and 1.5 inch, respectively. Find the required center distance
for the disks.
0.75

= 0.03125. The angle whose tangent is 0.03125 equals 1

degree 47.4 minutes; sin 1° 47.4' = 0.03123; 1.50 — 1.25 = 0.25 inch;
0.25

= 4.002 inches = center distance C.

2 X 0.03123

To Find Angle for Given Disk Dimensions. — When the diameters
of the large and small disks and the center distance are given, to de-
termine the angle a. Rule: Divide the difference between the disk
diameters by twice the center distance; find the angle corresponding
to the quotient, in a table of sines, and double the angle.

Example: — If the disk diameters are 1 and 1.5 inch respectively,
and the center distance is 5 inches, find the included angle a.
1.5 — 1

=0.05. The angle whose sine is 0.05 equals 2 degrees 52

2X5

minutes; then, 2 deg. 52 min. X 2 = 5 deg. 44 min. = angle a.
To Find the Taper per Foot. — When the diameters of the larg^ and
small disks and the center distance C are given, to determine the taper
per foot (measured at right angles to a line through disk centers).
Rule: Divide the difference between the disk diameters by twice the
center distance; find the angle corresponding to the quotient, in a
table of sines; then find the tangent corresponding to this angle, and
multiply the tangent by 24.

Example: — If disk diameters are 1 and 1.5 inch, respectively, and
center distance is 5 inches, find the taper per foot.
1.5 — 1

— = 0.05. The angle whose sine is 0 05 equals 2 degrees 52
2X5

26 - No. 130— GAGING TOOLS AND METHODS

minutes; tan 2° 52' = 0.05007; 0.05007X24 = 1.2017 inch taper per
foot.

Reference Gages

Reference gages are intended for testing the accuracy of working
gages such as are used in the shop and toolroom, and for setting other
forms of measuring instruments. Reference gages are made in dif-
ferent forms varying from plain blocks or disks to special shapes de-
signed for some particular class of work. The standard set of refer-
ence disks made by Brown & Sharpe contains 45 disks varying by
sixteenths of an inch, from ^4 to 3 inches in diameter. Handles are
provided so that these disks can be used in place of standard cylindrical
gages, but they are generally used without the handles for setting
calipers, testing measuring instruments and for reference purposes.

Fig. 19. Johansson Reference Gages

Plug and ring gages similar to the type illustrated at A, Fig. 16, are
also used to some extent for reference purposes, as well as for work-
ing gages. In some shops it is the practice to use the plug as a work-
ing gage and the ring for testing it, or, in case the ring is required
as a working gage, the plug is kept as a standard or reference gage,
as previously mentioned.

End-measuring rods and blocks are often used for testing snap
gages, etc. Ordinarily, the solid measuring rods are cylindrical in
form and may be obtained in sets covering a considerable range of
lengths. These rods are used for testing the parallelism and width
of two finished surfaces, as well as for setting calipers and testing
gages. The ends of some rods are made flat and parallel, whereas
others have ends which are sections of spheres, the diameters of which
equal the lengths of the rods. The spherical-ended form is very con-
venient for testing the diameters of rings, cylinders, etc. Some end-

GAGES

measuring rods are provided with an insulating handle in the center
to prevent expansion from the heat of the hand.

Johansson Gages

The Johansson combination standard gages consist of a series of
rectangular steel blocks which are finished on all sides with wonder-
ful accuracy. The opposite sides of each block are parallel and the
distance between them is equal to the dimension stamped upon the
block, within a limit so small as to be inconceivable. The eighty-one
blocks in what is known as Set No. 1 (see Pig. 19) are arranged in
four series. The first series contains 9 blocks which vary in thickness
from 0.1001 inch to 0.1009 inch, increasing by 0.0001 inch increments.
The second series contains 49 blocks varying in thickness from 0.101
inch to 0.149 inch, increasing by 0.001 inch. In the third series there
are 19 blocks varying in thickness from 0.050 inch to 0.950 inch, in-
creasing by 0.050 inch. The last series of four blocks has 1, 2, 3 and

Machinery

Fig. 20. Testing Size of Limit Gage with Johansson Gages

4 inch sizes, respectively. The gages for the English system of meas-
urement are adjusted to their sizes at 66 degrees F.

The value of these gages lies in the fact that they are not only
exceptionally accurate, but are so varied in size that, with the set re-
ferred 'to in the foregoing, a gage 10 inches long can be built and
dimensions varying by 0.0001 inch be obtained. According to the
makers, this one set will give at least 100,000 gage sizes, by using the
various combinations of blocks which are possible. Any dimension up
to 8 inches obtained by the systematic combination of these blocks is
said -to be exact within 0.00004 inch; hence, the error of any one
block is exceedingly small.

How to use Johansson Gagres

The combination of these Johansson gages to form any required
dimension is simple but should be done systematically. Every block
is marked with its size and in placing two blocks together they are
slid over each other with a slight pressure. Any dust that might be
on the surfaces should first be removed by using the finger. To illus-

No. 130— GAGING TOOLS AND METHODS

trate how the gages are combined, suppose 3.4566 inches is the re-
quired size. First it is well to consider the ten-thousandths in the
dimension; therefore, block 0.1006 (which is one ®f the first series
previously mentioned) would be selected. The thousandths in the
dimension are next taken care of by selecting block 0.106. The block

Machinery

Tig. 21. Method of accurately setting Work on Faceplate with
Johansson Gages

for the even number of inches, or the 3-inch size, is then added, which
makes the dimension 3.2066 inches; therefore, the block needed to
complete the dimension is 0.250. Thus, the entire set is made up as
follows: 0.1006 + 0.106 + 3 + 0.250 = 3.4566 inches.

This same dimension could also be obtained by using an entirely
different combination. In order to show how different combinations

Machinery

Fig. 22. Testing Location of Different Surfaces with
Johansson Gages

can be used for obtaining the same size, suppose the dimension 0.600
inch is required. Gages of this size could be made up by using the
following combination: 0.550 + 0.050; 0.450 + 0.150; 0.400 + 0.200;
0.350 + 0.250; 0.500 + 0.100, etc.

If a 1%-inch gage were required, the 1 inch, 0.500 inch and 0.125
inch blocks could be used. Thus: 1 + 0.500 + 0.125 = 1.625 or 1%

GAGES 29

inch. If a size 0.002 inch larger or 1.627 inch were required, this
could be obtained simply by substituting the 0.127 inch block for the
0.125 inch size. Other combinations could also be used for the size
given in the preceding example. From the foregoing, it will be
seen that a gage can be built up which will include the plus allow-
ance for a forced fit, the minus allowance for a running fit, or any
tolerance or limit which may be desired.

Application of Johansson Gagres

Fig. 20 indicates how these gages can be used for testing snap
gages and limit gages. When making a gage of the type illustrated,
the size can be followed by variations of 0.0001 inch as the jaws are
being lapped, and any tolerance or allowance for any class of fit can
be obtained. An entirely different application is shown in Fig. 21. In
this case the gages are used on a lathe faceplate in conjunction with
two parallels for locating work so that two holes can be bored accur-
ately with relation to each other. First hole C is bored with the
work resting against the parallels as shown to the left; then gages A
are inserted, thus moving the work over a distance Ax after which
gages B are placed beneath the plate to raise it a distance J?lf as
shown to the right. In this way the plate is located for boring a
second hole in accurate relation with the first hole.

These gages can also be used in conjunction with a surface plate
and surface gage for accurately scribing lines on die faces, etc. Thus,
instead of adjusting the pointer of the surface gage to different heights
by the use of a scale, the pointer can remain in a fixed position and
the work be accurately raised or lowered the required amount by
placing it upon different combinations of gages. In this way lines
can be laid out very accurately.

Fig. 22 shows still another application of these gages. In this
example the depths of different plane surfaces and the total thick-
ness of the piece are tested by using gages of the required sizes, in
conjunction with a straightedge which is placed across the top of the
work. These examples are simply given to illustrate a few of the
many ways in which these gages may be used.

CHAPTER IV

MISCELLANEOUS MEASURING AND GAGING TOOLS

The variety of gages required in most machine shops and toolrooms
is extensive, especially where many different classes of machines and
tools are manufactured, and gages of special design are often neces-
sary in addition to the standard measuring tools. Most of the com-
mercial gages and measuring instruments are designed to test or
measure the distance or angle between two points or surfaces, but
when there are several surfaces, all of which must be accurate with
relation to each other, a special form of gage is often designed. The
construction and arrangement of such a gage depends, of course, upon
the shape of the part to be tested and the location of the finished sur-

Machinery

Fig. 23. Universal Bevel Protractor

faces, and also upon the degree of accuracy required; therefore, in
this treatise, special types designed exclusively for one class of work
are not illustrated.

Measuring- Angles with a Protractor

The protractor is an instrument used for measuring angles. There
are many different forms of protractors, but they all embody the same
general principle. The type commonly used by machinists and tool-
makers has a straightedge or blade which can be set at any angle
with the base or stock, and the angle for any position is shown by
degree graduations. This form is generally known as a bevel pro-
tractor. A design of bevel protractor that has been extensively used

ANGULAR MEASUREMENTS

is shown in Fig. 23. The angular position between blade A and stock
B can be varied as may be required, and disk C, which is graduated
from 0 to 90 degrees in each direction, shows what the angle is for
any position. The blade, which is clamped by an eccentric stud, can
be adjusted in a lengthwise direction so that it can be used in any
position. Fig. 24 illustrates some of the various ways in which this
universal bevel protractor can be applied.

Reading- a Protractor Vernier

The graduations on the protractors commonly used by machinists
are ordinarily not finer than whole degrees, so that measurements of

Machinery

Fig. 24. Examples Indicating Application of Universal
Bevel Protractor

fractional parts of a degree cannot be made with accuracy. By the
addition of a vernier scale, subdivisions of a degree are easily read.
The vernier scale of a universal bevel protractor is shown in Fig. 25.
This particular vernier makes it possible to determine the angle to
which the instrument is set, within five minutes (5') or one-twelfth
of a degree. It will be noted that there are practically two scales
of twelve divisions each, on either side of the vernier zero mark. The
left-hand scale is used when the vernier zero is moved to the left of
the zero of the true scale, while the right-hand scale is used when the
movement is to the right. The total length of each of these vernier

No. 130— GAGING TOOLS AND METHODS

scales is equal to twenty-three degrees on the true scale, and as there
are twelve divisions, each division equals 1/12 of 23 or 1 11/12 degree.
One degree equals 60 minutes (60'), and 11/12 degree equals 11/12
of 60 or 55 minutes; hence each division on the vernier expressed in
minutes equals 60' + 55' = 115 minutes. Now as there are 120 minutes
in 2 degrees, we see that each space on the vernier is 5 minutes

Fig. 25. Protractor Scale and Vernier

shorter than 2 degrees; therefore, when the zero marks on the true
and vernier scales are exactly in line, the first graduation (either to
the right or left) on the vernier is 5 minutes from the first degree
graduation; the next two are 10 minutes apart; and the next two 15
minutes, etc. It is evident then that if the vernier is moved, say to
the right, until the third line from zero is exactly in line with one

Fig. 26. Diagrams showing how Sine-bar is used for Measuring Angles

on the true scale, the movement will be equal to 15 minutes, as indi-
cated by the number opposite this line on the vernier.

To read the protractor, first note the number of whole degrees
passed by the vernier zero, and then count in the same direction the
number of spaces between the vernier zero and that line which exactly
coincides with one on the regular scale; this number of spaces multi-
plied by 5 will give the number of minutes to be added to the whole
number of degrees. The reading of a protractor set as illustrated in
Fig. 25 is 12 whole degrees plus 40 minutes. The vernier zero has
passed the twelfth graduation and the eighth line on the vernier

ANGULAR MEASUREMENTS

coincides with a line on the true scale; hence, 40 minutes is added to
12 degrees to get the correct reading.

Sine-bar for Measuring Angles

The sine-bar is used either for measuring angles accurately or for
locating work to a given angle. It consists of an accurate straight-
edge to which are attached two hardened and ground plugs p and p{
(see Fig. 26). These plugs must be of the same diameter, and the

Fig. 27. Setting Sine-bar with Micrometer Gage

distance I between their centers should, preferably, be an even dimen-
sion, to facilitate calculations. The edges of the straightedge must
be parallel with a line through the plug centers. The sine-bar is
always used in conjunction .with some true surface B from which
measurements can be taken. Two methods of measuring an angle
are illustrated. Referring to the left-hand sketch, the upper edge A
of the part to be measured is set parallel with surface plate B. The
heights a and b from the surface plate to the plugs p and p^ are
carefully measured either by using a micrometer gage or a vernier
height gage. The difference between a and Z> is determined, and this
difference, divided by the length I between the plugs of the sine-bar,
equals the sine of the required angle /3. The angle is then found by

34 No. 130— GAGING TOOLS AND METHODS

referring to a table of sines. For example, suppose length I is 10
inches, height a, 7.256 inches and height &, 2.14 inches; then the sine
of the required angle equals (7.256 — 2.14) -^ 10 = 0.5116, which is
the sine of 30 degrees 46 minutes. A 10-inch sine-bar is convenient
to use, as division can be performed mentally by simply moving the
decimal one point to the left. Fig. 27 illustrates how the sine-bar A
is used to determine the angle between the lower edge of triangle B
and the machine table. A micrometer gage is used for measuring the
vertical heights of the plugs.

The sketch to the right in Fig. 26 illustrates a method of measuring
an angle without first setting one edge parallel to surface B, the
angle of each edge being measured separately. Suppose the height d
equals 8.75 inches and c equals 6.5 inches. Subtracting c from d:
8.75 — 6.5 = 2.25. Next shift the sine-bar to the position shown by
the dotted lines. Assuming that e = 5 inches and / = 2.15, then e — /
= 5 — 2.15 = 2.85. Dividing 2.25 and 2.85 by 10 (or the center dis-
tance between the sine-bar plugs) we get 0.225 and 0.285 as the sines
of the angles; 0.225 is the sine of 13 degrees 1 minute, and 0.285 is the
sine of 16 degrees 34 minutes. The sum of these angles or (13°!') -f
(16° 34') =29 degrees 35 minutes or the required angle 7.

When the sine-bar is to be set to a given angle for locating some
part with reference to it, it is first set approximately. The sine of
the required angle is then found and this s*ine is multiplied by the
distance I between the plug centers, to obtain the vertical distance x
(see left-hand sketch Fig. 26) for that particular angle. The bar is
then adjusted until the vertical distance x coincides with the dimen-
sion found. For example, if edge A is to be ground to an angle of 30
degrees 46 minutes from edge E, the sine-bar is clamped to the angle-
plate at approximately this angle. The sine of 30 degrees 46 minutes,
or 0.5116, is then multiplied by 10 to obtain the vertical distance x,
and the bar is adjusted by the use of a vernier height gage until x
equals 0.5116 X 10 = 5.116 inches.

Machinists' and Toolmakers' Squares

The squares used by machinists and toolmakers are such common
tools that it seems unnecessary to illustrate them. There are two
types of fixed tri-squares in common use. One type has a narrow
blade of rectangular section and the beam or stock, as well as the
edges of the blade, are hardened to prevent inaccuracy as the result
of wear. The other type of square is intended for very accurate
work. The blade is beveled on both edges so that practically a line
contact with the work is obtained. (The adyantage of the line con-
tact as compared with a surface contact is explained in the paragraph
on straightedges.) There is also the tool known as a "combination
square" which is a type that is extensively used. It includes in
addition to a square a protractor, a scale, and a center-head for locat-
ing the edge of the scale in line with the center of a shaft, etc.

Two methods of testing the accuracy of a tri-square are shown in
Fig. 28. In order to make a reliable test, a 90-degree angle should

ANGULAR MEASUREMENTS

be originated, unless a master square of known accuracy is available.
A comparatively simple way of doing this accurately is to make a
cylindrical plug similar to the one shown at A. The lower end of
this plug is recessed to form a narrow edge which is beveled on the
outside so that there will be no bearing in the corner where the
blade joins the stock. This plug is ground on dead centers and
lapped to form as perfect a cylinder as possible. The narrow edge at
the end is then ground true so that it will be exactly at right angles
to the cylindrical surface. By holding the square against the side
and end of the plug, as the illlustration indicates, and subjecting it to
the light test, a very minute inaccuracy in the position of the square
blade can be detected. The outside edge of the blade can be tested by
placing the plug and square on an accurate surface plate, and bring-
ing the blade edge into contact with the side of the plug.

-i

Machinery

Fig. 28. Two Methods of Testing a Square

A more elaborate form of test block but one which gives very
accurate results is shown at B, Fig. 28. This test block is formed
of a square cast-iron frame which is grooved around the outside and
contains four close-fitting adjustable strips which, in the illustration,
are numbered from 1 to 4. The reliability of this test block depends
largely upon the outer edges of these strips which must be accurately
finished plane surfaces. The strips are held in place by close-fitting
pins c near the ends, and by bolts d. The latter pass through clear-
ance holes in set-screws e which are screwed through the frame and
bear against the inner edges of the strips. By clamping one of these
strips against the set-screws, it is locked in position after being
properly adjusted.

The method of using this test block for determining the accuracy
of a tri-square is as follows, assuming that the edges have not previ-
ously been adjusted: The square is first placed against two of the
strips or straightedges of the test block. These strips are then ad-
justed until they exactly fit the square being tested. If the square

No. 130— GAGING TOOLS AND METHODS

were first applied to strips Nos. 1 and 2 (as shown in the illustration)
strips 2 and 3 would next be set in the same manner, and then strips
3 and 4. After making these adjustments, if the square is applied
to the strips Nos. 4 and 1, any error which might exist would be
multiplied four times; whereas, if the square fitted these last sides
perfectly, this would indicate that the angle between the square
blade and stock was 90 degrees, within very close limits.

To illustrate how the error accumulates in going around the test
block, suppose the angle between the blade of a square and its stock
were 90 degrees 15 minutes. Evidently, then, sides 1 and 2 of the
test block would also be set to this angle. Therefore, taking side No.
1 as a base, side No. 2 would be out 15 minutes. As side 2 is used in
setting side 3, the error of the latter with reference to side 1 would
be 30 minutes; similarly, side 4 would have an error of 45 minutes,

and when the square was applied to
sides 4 and 1 for the final test, the
error would be four times the orig-
inal amount, or 1 degree.

In order to originate a 90-degree
angle, or, in other words, to set the
test block to this angle, a sheet steel
templet is used. This simply forms
a temporary tri-square and is cut
away so that there are two small pro-
jections along each test edge, in
order that changes can be made by
simply altering these small projec-
tions. This templet is first made as
accurately as possible and it is them
used in setting the test block. After adjusting the block, if compari-
son with the fourth and first sides shows an error, the templet is cor-
rected and the test block again adjusted. This operation is repeated
until the 90-degree angle is originated. The accuracy of a square can
then be tested by comparison with any two sides of the test block and
without making any adjustments.

Straig-htedses

Straightedges are used to test flat surfaces for determining whether
or not they are true planes, and also for testing round parts for
bends, or curvatures in a lengthwise direction. Perhaps the most
common form of machinists' straightedge is of rectangular section, as
shown at A, Fig. 29. In order to increase the sensitiveness of a
straightedge for showing minute deviations or curvatures,, the test-
ing edge is made narrower by beveling one side as shown at B, thus
decreasing the width to about 1/16 inch. For work requiring extreme
accuracy, the form of straightedge shown at C is commonly used.
The testing edge is very narrow and is of semi-circular cross-section
so that a line contact is obtained instead of a surface contact, as with
the form having flat edges. This line contact shows any minute

Fig. 29. Three Types of
Straightedges

HEIGHT AND DEPTH GAGES

curvature which may exist and as the edge is curved the accuracy of
the test will not be affected if the straightedge is not held exactly
at right angles to the surface being tested. When using a straight-
edge having plane or flat surfaces, it should be held square with
the work, because, if canted so that only one edge is in contact, any
inaccuracy along this edge would appear as an inaccuracy in the sur-
face being tested. When comparing a surface with a straightedge,
there should be a good light on the side opposite the observer so that
any irregularities or curvatures in the work can readily be detected.

Heig-ht and Depth Gages

The vernier height gage, shown at A, Fig. 30, is used for locating
jig buttons, measuring the vertical distance from one plane surface

Fig. 30. (A) Vernier Height Gage. (B) Vernier Depth Gage

to another, etc. It is similar to a vernier caliper, except th'at there is
a rather heavy base which allows the gage to stand upright. The
movable jaw of this particular make of gage has a projection which
extends beyond the base and is convenient for testing the height of
a button attached to a jig plate (as the illustration indicates) and
for similar work. The end of this extension is beveled to a sharp
edge for scribing lines. The gage is graduated to read to thou-
sandths, by means of a vernier scale on the sliding jaw. There are
graduations on both sides, giving readings on one side for outside
measurements and on the other side for inside measurements. This
particular gage can be used for heights up to 8 inches.

Illustration B, Fig. 30, shows a depth gage for measuring the depths
of holes, recesses in dies, etc. The vertical blade or scale is gradu-
ated and by means of a vernier gives readings to thousandths of an
inch. Height and depth gages are also made on the micrometer

No. 130— GAGING TOOLS AND METHODS

principle; that is, instead of having a scale and vernier, the adjust-
ments are effected by a micrometer screw, graduated to read to
thousandths.

The Surface Gagre

The surface gage is used extensively for scribing lines that repre-
sent finished surfaces, and also for testing the parallelism between a

surface and the table of a machine, such
as the planer or shaper. A common form
of surface gage is shown in Fig. 31. It
has rather a heavy base on which is
mounted a rod carrying a pointer or
scriber 8. The latter can be adjusted in
or out and it can also be moved to any
position along the rod. After the scriber
or pointer has been set to about the right
height, it can he set accurately to the
position desired by turning screw A,
which gives a fine adjustment. There
are two pins B in the base which can be
pushed down when it is necessary to keep
the gage in line with a finished edge or
the side of a T-slot in the planer table.

When using the gage to set a surface
parallel with the table of a planer or
is first set to just touch the work at
some point. The gage is then placed in different positions in order
to compare the height at various places. The surface gage is also

Machinery

Fig. 31. Surface Gage

other surface, scriber 8

Machinery

Fig. 32. Plan View Illustrating use of Center Indicator

extensively used for scribing parallel lines when laying out the
work, scriber S being reversed to locate the straight or sharp end
in front. This pointer is also useful for setting lines representing
finished surfaces, prior to the planing operation.

TEST INDICATORS

Center Indicator

The center indicator is used to set any point or punch mark in line
with the axis of a lathe spindle preparatory to boring a hole. The
plan view, Fig. 32, shows how the indicator is used. It has a pointer
A, the end of which is conical and enters the punch mark to be cen-
tered. This pointer is held by shank B which is fastened in the tool-
post of the lathe. The joint (7, by means of which the pointer is held
to the shank, is universal; that is, it allows the pointer to move in
any direction. When the part being tested is rotated by running the
lathe, if the center punch mark is not in line with the axis of the
lathe spindle, obviously, the outer end of pointer A will vibrate, and
as the joint C is quite close to the inner end, a very slight error in

Fig. 33. Testing Concentricity of Roller Bearing, -with
Dial Test Indicator

the location of the center punch mark will cause a perceptible move-
ment of the outer end, as indicated by the dotted lines. Obviously,
when the work has been adjusted until the pointer remains practically
stationary, the punch mark is in line with the axis of the lathe
spindle. When two holes are being bored to a given center-to-center
distance, by first -laying out the centers and then indicating them
true in this way, the accuracy depends largely upon the location of
the center punch marks.

Test Indicators

The test indicator is extensively used in connection with the repair
or erection of machinery, for detecting any lack of parallelism be-
tween surfaces, in inspection departments, and for testing the ac-
curacy of rotating parts (such as spindles or arbors) in connection
with general machine shop work. Fig. 33 shows how a dial indicator

No. 130— GAGING TOOLS AND METHODS

is used to test the concentricity of the outer race of a roller bearing.
The assembled bearing is mounted upon an accurately running arbor,
held between centers, and the contact point A of the indicator bears
against the surface of the outer race. As the latter revolves, the
slightest deviation or eccentricity is shown by vibrations of the dial
hand, which is so connected with the contact point that any motion
of the latter is magnified a number of times. The graduations on the
dial face indicate thousandths of an inch, and the dial is adjustable
so that it can be turned to locate the zero mark directly under the

Machinern

Fig. 34. Examples Illustrating use of Test Indicators

hand, after the contact point has been adjusted against the work.
The graduations then give a direct reading in thousandths for any
deviation from the central or zero position. The contact point is re-
movable to permit inserting different forms.

In this particular case, the indicator is supported by a vertical rod
attached to a base B, which forms part of the instrument. It is often
used independently of the base, as when held in the toolpost of a
lathe for testing the accuracy or concentricity of a cylindrical sur-
face. The dial indicator is also used for many other purposes. For
instance, it is often attached to a surface gage, in place of the pointer

SPECIAL GAGES 41

or scriber, for testing the parallelism of a surface, especially when
it is desirable to know the exact amount of inaccuracy. This form
of indicator is also useful for testing the parallelism between the
cross-rail and table of a planer. To make a test of this kind the indi-
cator is held in the toolpost and the slide is lowered until the contact
point bears against the table. The dial is then turned until the zero
mark coincides with the indicating hand, and, when the gage is
traversed across the table by moving the toolhead along the cross-
rail, any inaccuracy is shown by the movement of the hand away
from the zero position. Of course, it is not necessary to adjust the
dial to the zero position, but this is advisable as the reading can
then be taken direct from the dial graduations. This form of indi-
cator is often used on milling machines or shapers for setting the
jaws of a vise or the side of an angle-plate exactly parallel to the line
of feeding movement, and for many other similar purposes.

Two other forms of test indicators are shown in Fig. 34. This type
is also used in connection with the erection or inspection of ma-
chinery for detecting inaccuracies, such as the lack of parallelism
between two surfaces or the amount a cylindrical part runs out of
true. Diagram A illustrates how a jig button is set true with the
lathe spindle. The point of the indicator is set against the button
and, as the latter revolves, any inaccuracy is shown by the vibrations
of the pointer. Any movement of the contact point is multiplied
several times by the pointer, and graduations at the end of the latter
indicate thousandths of an inch.

Diagram B illustrates how another test indicator of different form
is used for determining the accuracy of a spindle in relation to a
T-slot in the bed. A true arbor is inserted in the spindle and the
contact point of the indicator bears against it. Any inaccuracy is
shown on a greatly increased scale by the pointer, the end of which
may be seen at the right end of the indicator body.

While these two indicators differ in construction they operate on
the same principle and are used for the same class of work. There
are also many other forms or designs of this same general type.

Special Indicating- Gages

The dial indicator is used in combination with many different gag-
ing devices, for testing the accuracy of finished parts. Fig. 35 shows
a gaging fixture which is used for testing the inside diameters of
the inner races of ball bearings. The race to be tested is placed over
a stud at the left end of the gage, as shown in the illustration. This
stud has a two:point bearing and the gaging arm forms the third
point. A multiplying lever extends to the other end of the fixture
and the end of this lever bears against the plunger of a dial gage,
which shows any variation in the diameter. Errors above or below
the standard size are multiplied ten times so that the gage, which
normally reads to thousandths, gives a direct reading to 0.0001 inch.
By adjusting the dial so that the hand points to zero, when the gage
is set to the standard size, the amount of variation either above or

No. 130— GAGING TOOLS AND METHODS

below this standard dimension is easily determined. Thus it will
be seen that gages of this type are "comparators" that show varia-
tions from a standard size but are not used for taking measurements.
Another form of dial gage for testing the outside diameters of

Fig. 35. Internal Gaging Fixture for Ball Bearing Races

finished ball 'bearings is shown in Fig. 36. This gage consists of a
multiplying lever, one end of which comes into contact with the
work while the other end bears against the plunger of the dial gage.
The test is made by simply rolling the bearing on the true base of

Fig. 36. Gage for Testing Outside Diameters of Ball Bearings

the fixture and under the end of the multiplying lever. Obviously,
any variation from the standard size to which the gage is set, is in-
dicated by the dial. The arm which carries the multiplying lever can
be adjusted vertically in the slotted supporting bracket in order to
set the gage for testing different sized bearings. The exact adjust-
ment of the gage is obtained by comparing it with a master disk, such

SECTIONAL GAGES

as the one shown to the right of the illustration. This disk is also
used for checking the gage at intervals, to insure accurate readings.
A great many special gages of the same general type as those
shown in Figs. 35 and 36 are now used, especially in inspection de-
partments. A common idea of a gage is that it should have gaging
surfaces which are a duplicate or exact complement of the part to
be tested. A thread plug gage, for instance, is often regarded as
being properly a steel plug threaded and hardened, the thread shape
conforming exactly to that of the standard thread. While manufac-
turers furnish gages of this type in response to common demands,
it is well known that such a gage is not a properly designed testing
instrument. It is true that the ordinary thread plug gage may
answer the purpose for which it was designed and it is also true that
it is hardly practicable to devise a low-priced gage in which the
faults of the plug gage are eliminated. The plug gage satisfies the com-
mon demand for a standard
form that can be referred to for
all dimensions, angles and
shapes. A gage, however, which
is used to test, at the same time,
all the dimensions of even a sim-
ple part, is likely to be inaccur-
ate and unreliable. As a gen-
eral principle, a cylindrical plug
gage should never *e required to
measure more than on diameter,
and a solid gage should not be
made to verify the concentricity
of more than two cylindrical
surfaces simultaneously. Some

f\ ||jj

* M f I *

I r-i I

Fig. 37, Sectional Gages

gages cover so many surfaces that it is impossible to determine
definitely where the inaccuracies are; moreover, a gage of this type
may seem to fit perfectly Vhen in reality there are errors which
remain undetected. A thread gage which is in the form of a threaded
hole may seem to fit a screw perfectly and yet the screw may be
several thousandths of an inch under size. For instance, if there is
an error in the lead of the thread this may cause a screw that is
under size to fit into the gage without perceptible play.

The type of gage having movable parts connecting with gradu-
ated dials, so that plus or minus readings can be taken directly, has
replaced many gages of the fixed type, especially for inspection work,
because they give a direct comparative measurement within very
small limits of accuracy. Such gages, however, are often quite
expensive and, in many cases, simpler forms serve all practical
requirements.

Sectional Gagres

A sectional snap gage formed of four parts is shown in the upper
part of Fig. 37. The measuring jaws, instead of being integral with

44 No. 130— GAGING TOOLS AND METHODS

the gage body, are attached to a central block by screws, as shown.
The width a of one end of this central block equals the size of the
"go" end of the gage; width & equals the size of the "not go" end.
The gage jaws are made flat. The advantage of this design, as com-
pared with a solid snap gage, is that when the accuracy is impaired
as the result of wear the gage can be restored to its original accuracy
by simply removing the gage jaws and truing them by grinding and
lapping.

The same principle can also be applied to an angular taper gage,
as shown by the lower view, Fig. 37. The gage jaws are attached to
a central block B finished accurately to the required taper, and the
size of the work A is tested by pushing it between the jaws and
noting the position of the end relative to a standard graduation mark.
When the gage becomes inaccurate, as the result of wear, the jaws
are removed and trued. A master plug should be used, occasionally,
for testing the accuracy of the gage. By having one jaw graduated,
as shown, the amount of inaccuracy may also be gaged, by noting how
far the end of the work comes short of or projects beyond the stand-
ard dimension mark.

Spirit Levels

Levels are frequently used by machinists especially when erect-
ing engines or heavy machinery. The accuracy of a spirit level
depends entirely upon the curvature of the glass tube. This tube
is ground on the inside to a barrel shape, except in cheap levels
which simply have a glass tube bent to the approximate curve. The
bent tube type is not to be recommended except for work which does
not require great accuracy. The tube is nearly filled with spirits of
wine, ether or some similar fluid and is hermetically sealed at each
end. The larger radius of curvature the glass has, the more sensitive
will be the level. The air space in a ground glass is much longer
than in a bent one, being ordinarily from 1/4 to 1/3 the length of
the tube. Modern levels are graduated to tenths and twentieths of
an inch, except when they are divided according to the metric system.
The angular value of a division may be determined roughly as fol-
lows: Support the level upon a piece of metal, the lower surface
of which has been filed or cut away so that it bears on two points
exactly 12 inches apart. Insert packing under one of the bearing
points to bring the air space near the center. Note carefully where
the air space is and then put a "feeler gage," say, 0.002 inch thick,
under one of the bearing points; then if the air space moves, say,
one-tenth inch, the angular value in seconds for one division of the
level is found as follows: The distance from the bearing point to
the feeler gage is 12 inches, which is the radius of a circle the cir-
cumference of which is 75.3984; hence 75.3984 inches is equivalent
to 1,296,000 seconds angular measurement. Therefore, 0.002 inch
equals 34.3 seconds and each one-tenth inch on the level also equals
34.3 seconds. The angular value of the graduations can, in this way, be
determined.

MEASURING MACHINE 45

A good level is a very sensitive instrument and should be carefully
used. The leveling glass or "bubble" is generally fixed in a brass tube
with plaster-of-paris. This method is satisfactory for all levels having
an accuracy of about five seconds angular measurement to each one-
tenth inch graduation. For finer levels, it is better to fix one end
only with plaster-of-paris and the other end with cork, for if the glass
is fixed rigidly at both ends with plaster-of-paris, there will be a strain
on the level due to temperature changes, and as the expansion of glass
and brass is different, a slight inaccuracy is liable to result. It is also
advisable to have an extra glass tube surrounding the leveling tube
for very accurate levels, in order to provide insulation from the heat
of the hand. A level of one minute angular measurement to one-tenth
inch graduation is the most serviceable for general use.

Measuring1 Machines

The measuring machine is an instrument of great precision that is
used for originating standard lengths and for verifying the accuracy
of reference gages. It might properly be defined as an instrument
for obtaining accurate subdivisions of the standard Imperial yard,
which is the basis of the English system of measurement. The Pratt
& Whitney measuring machine is shown in Fig. 38. This machine
has a heavy cast-iron bed upon which two heads are mounted. One
of these heads, A, is normally fixed to the bed, whereas the other
head, B, is adjustable along the accurately machined ways of the bed,
for the measurement of various lengths. Each head has a spindle
or measuring point and the part to be measured is supported between
these spindles upon the rests C, which are of suitable shape at the
top to center the work. Measurements up to 1 inch are obtained by
means of a large graduated index wheel D, a scale and pointer at H
being provided for approximate setting. For lengths greater than
1 inch, the sliding head is set by means of a standard bar E at the
rear. (See Fig. 39.) The divisions or graduations, which are exactly
1 inch apart, are marked upon the surfaces of plugs set into this bar
and are so fine that they are imperceptible to the naked eye. The
sliding head is located for the inch positions by adjusting it with
reference to these lines. In order to secure an adjustment which will
exactly conform to the divisions on the standard bar, the sliding head
is equipped with a powerful microscope F which is provided with a
very fine line which is set with reference to the bar graduations. The
screw of the sliding-head spindle, by means of which the adjustments
for fractional parts of an inch are obtained, has twenty-five threads
per inch, and the index wheel D has 400 graduations on a machine
for English measurements; therefore, each graduation represents a
1/400 of 1/25 or 0.0001 inch, and the divisions can easily be sub-
divided into quarters or even less by estimation.

In order to insure a light contact or delicate and uniform pressure
between the measuring points each time a measurement is taken, the
machine is provided with a simple indicating device on the fixed
head. This consists of two auxiliary jaws between which is held a

No. 130— GAGING TOOLS AND METHODS

MEASURING MACHINE

special end-measuring bar or gage 10.2508 inches long. First the
machine should be set in the zero position with the measuring points
in contact. In order to do this, adjust the screw of the linear scale
at the top of the head to zero, and set the pointer of the index wheel
D nearly to zero; then slide the head until the measuring faces are
almost in contact, and then by means of screw J, at the right of the
head, adjust one spindle against the other until the indicating plug G
shows a tendency to move from its horizontal position. Next clamp
the head firmly and adjust the index wheel until the plug G swings
down to a vertical position. Then set the adjustable index
pointer to zero, and the line in the eye-piece of the microscope so
that it exactly coincides, with the zero line of the graduated reference
bar E, Fig. 39, at the rear. The adjustment of the line in the eye-
piece is made by means of screw K. The machine is now set in the

Fig. 39. Rear View of Pratt & Whitney Measuring Machine

zero position, and, when adjusting the head for the required measure-
ment, care must be taken not to disturb the eye-piece of the microscope.
To measure from zero to one inch, the micrometer screw can be
used direct, but for greater dimensions locate the sliding head so
that the line in the eye-piece of the microscope coincides with the
graduated plug from which the measurement is to be taken, the fine
adjustment necessary being obtained by means of screw J at the
right of the head. In this particular case, the head would be moved
back along the bed until the line in the eye-piece of the microscope
exactly coincided with the tenth graduation line. The distance be-
tween the measuring surfaces is now 10 inches. As the length re-
quired is 10.2508 inches, the screw would be turned back until the
scale and index wheel of the adjustable spindle showed a movement
of 0.2508 inch. As the pitch of the screw is 1/25 inch, each complete
turn of the index wheel equals 0.040 inch; hence, for a movement of

48 A Ko.. 130- -CAGING TOOLS AND METHODS

0.2508 inch, the turns of the index would equal 0.2508 -f- 0.040 = 6.27,
or six full turns and 108 divisions.

To test the rod, the index wheel would be turned a little beyond
the required distance and the rod placed between the measuring sur-
faces. After setting plug G in a horizontal position, the index wheel
would be turned back to the 10.2508 position. If plug G dropped be-
fore this position was reached, it would indicate that the rod was too
long, but if it remained in a horizontal position, it would show that
the rod was under size. In either case, the exact amount of error
could easily be measured. When measuring an end gage, especially
if of considerable length, care should be taken to prevent any varia-
tion in the temperature of the gage. When it is desired to test one
gage with another master gage, the machine is first set by adjusting
the contact points with the master gage. The other gage is then
placed between the jaw:s and its length compared by referring to the
graduations on the machine.

The Pratt & Whitney machines graduated for English measure-
ments are standard at 62 degrees F. It is not necessary, however,
to use the machine at this initial temperature, because variations
due to temperature changes will affect both the work and the machine
practically the same, although when the machine is used for scientific
research, the initial temperature should be adhered to.

Measuring: Large Diameters

The accurate measurement of exceptionally large diameters is rather
difficult because of the spring or deflection of the measuring instru-
ment. The operation is often further complicated when using a gag-
ing tool not provided with graduations giving a direct reading, owing
to the difficulty of obtaining the exact length of a diameter, in feet and
inches, after the gaging tool has been set. A fairly accurate method
of determining the external diameter of a large circular part is to
first measure the circumference with an accurately graduated steel
tape and then divide the reading by 3.1416 to get the diameter. One
advantage of measuring large work in this way is that the reading is
magnified 3.1416 times, each inch of diameter being represented by
this number of inches on the tape; hence, the diameter can be de-
termined quite accurately provided a high-grade steel tape is used.
A large internal diameter can also be measured by this method, when
the outside and inside surfaces are finished concentric, by first meas-
uring the circumference with a standard steel tape and then deduct-
ing from the diameter thus obtained twice the thickness of the wall
between the inner and outer surfaces. The Pratt & Whitney car
wheel circumference gages are made of flexible tempered steel ribbon,
and are graduated to give, by circumference measurement, the standard
diameters of car wheels varying from 24 to 42 inches. These gages
are provided with adjustable handles for holding the ribbon or tape
about the wheel.

UNIVERSITY OF CALIFORNIA LIBRARY
This book is DUE on the last date stamped below.

AinOBlSCClRC WR 31*9

OCT16 194/

LD 21-100m-12,'46(A2012sl6)4120

U.C.BERKELEY LIBRARIES

UNIVERSITY OF CALIFORNIA LIBRARY

MACHINERY'S

HANDBOOK

For MACMV f HOP
AND DRA* )M

A REFERENCE '*OOK jl "'ACHINE

DESTGN AND SHOr ™ : iCE FOH

THE M5CHA1, 0 vL > JINEF '*,

DRAFTSMAN, T^ -, W ER A
MACHINIST.

Handbook comprises nearly 1400 pages of carefully edited and
condensed UK; • •. •'< \ the theory and practice or the machine-building

industries. If: is the first and only complete handbook devoted exclusively to
the m*:t;i.l-\vi 1 -n^ fiek1, and conf.nins in compact and condensed form the
information :.•• fl.itn (.•• ,11 rted by MACIIIM I:Y durimr the pa&i twenty ye; .s.
It is iiif ()• i •!• ; in a library of mf-vhaifur1 literature, because it

Cuntai; :• all th; -faii("> in the text-books and i realises on mechan''-al

eiii?inoeriiip pr.M... 10.

GENERAL CONTENTS

Mathematical tablor "" c.ipnl ir;cUiO'1 and formulas ! i arithmetic ^atl algebra —
Loe-vi-'thms and lo^; : anJ volumes — Solution of ^nangles and

tritoouometrical tabl . opositions and problems — Moohanics — Strength of

materials — I »^.tinj, .. r --Strength and properties of steel wire — Strength

and j . ..^ertiea o' - i>e ropu— - or :as and tables for spring design — Torsional strength

— Shaiting — Friction — Plain, roller a-;d hall bearingi — Keys ar,,l key ys — Clutches and
couplings — Fr;"tion "brakes — Oa"is, *m design and <iam milling — Spur scaring — Bevel
gearing — Spiral gearing — IT •u.gbon gearing — Worm fearing- Epiryolic Bearing — Belting
and rope drives — Transmission chaii. and chain drives — Crane uhain — Dhr.ensions of small
machine details — Speeds and -" ~ls rf machine tools — Shrinkage and force fit allowances —
Measuring lools ami gaging -thods — Change gears for spiral milling — MJil.ng machine
indexing- -Jigs and fixtures — ./rinding >i"d grinding v/hools — Scrov thread systems and
thraad gages — laps and th eading dies — Milling cutlers — Ueaners, covnterbores and
twist drills — Heat-treatment of steel — Hardening, casehardening. Annealing — Testing the
hardness of metals — Foundry and pattern shop information — The welding of metals —
Autogenous welding — TLermit welling — Machine welding — BJacksjnitn shop information

— Die casting — Extrusion process — Soldering and brazing- — Etching and etching fluids —
Coloring metals — I." ichin r 1 mndations — Application of motors t< nachine tools — Dynamo
and motor tro-iblos — W. ts and measures — Metric system — C nrsicn i.aMes — Specific
gravity — Wei^uts of r1" -ials — Heat — Pneumatics — Water pres u'f »nc. (low of water-
Pipes and i.-pi»".' — Lute- and cements — Patents.

F"vemNF.i<\. the leading journal in tlie machine-building field. tl;e originator
of the 25-cent Ref • rence and ata Bo^ks. Publisln moi rhl: fubscript; .u,
$2.00 yearly. Foreign sni;s« 7ij-,-;,ion, $3.0^

TM »NOUSTRIAL PRESS, Publishers oi t,^\..

140-1 i

«TTE STREET

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R CITY, U. S. A.

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